1. Technical Field
The present invention relates to a technique for sealing a thin film of a light-emitting element.
2. Related Art
As one type of light-emitting elements, there is an organic EL (electroluminescent) element that has a multilayered structure of two electrodes and a thin organic light-emitting film, formed of an organic compound, interposed between the two electrodes and emits light by excitation due to an electric field generated between the two electrodes. A sealing process is performed to prevent an organic light-emitting material and a cathode, which includes an electron injection layer formed of, for example, calcium, magnesium, or aluminum complex, from deteriorating. As sealing techniques, a thin-film sealing technique for covering organic EL elements with an excessively thin inorganic compound film has been known (see JP-A-9-185994, JP-A-2001-284041, JP-A-2000-223264, and JP-A-2003-17244). In these techniques, the inorganic compound film serves as a gas barrier layer that prevents the infiltration of air.
In the thin-film sealing technique, in order to cover the organic EL elements, a planarizing layer formed of an organic compound, such as an organic buffer layer, is formed on the surfaces of cathodes of a plurality of light-emitting elements and on pixel partitions to planarize uneven portions formed by the cathodes and the pixel partitions, and then a gas barrier layer formed of an inorganic compound is formed thereon. However, in the gas barrier layer having the above-mentioned structure, stress concentrates on the edge of the organic buffer layer (a rising portion of the organic buffer layer). When remarkable stress concentration occurs, the gas barrier layer may be cracked or peeled off. Further, when a gas barrier layer is formed of an inorganic compound, such as silicon compound having transmittance and high moisture-resistance, the inorganic compound layer has density and elastic modulus (Young's modulus) higher than those of an organic compound layer. Accordingly, a crack may occur due to the stress concentration.
If the gas barrier layer cracks or is peeled off, moisture contained in atmospheric air is infiltrated into the organic EL elements, which causes the sealing property (in particular, coatability for minute foreign materials not purified by a clean room) of the organic EL elements to significantly deteriorate. This causes early deterioration of the organic EL elements, which will be necessarily solved. When a gas barrier film is composed of an organic compound film having low elasticity to prevent the stress concentration, or when the gas barrier layer is formed with a constant thickness to prevent the stress concentration, the gas barrier layer is not cracked or peeled off, but a sufficient sealing property is not obtained, which will cause early deterioration of the organic EL elements.